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Prehistoric Aggie: USU Geologists Celebrate Namesake Trilobite

Thursday, Jan. 12, 2012


Tiny Zacanthoides liddelli, a trilobite that existed some 520 million years ago, is named for USU geologist Dave Liddell.

Dave Liddell and Bob Gaines doing fieldwork

Dave Liddell, left, professor and head of USU's Department of Geology, and colleague Bob Gaines of the University of California, Pomona, rest on an outcropping of the Spence Shale Formation in Utah’s Wellsville Mountains.

In recognition of nearly 20 years of field work in Utah’s ultra-steep Wellsville Mountains, along with exhaustive classification and sedimentation modeling of Cambrian formations, Utah State University geology professor Dave Liddell has a prehistoric namesake.

Zacanthoides liddelli is the prodigious name given to the spiky little critter. The newly identified species of trilobite is described and named by paleontologists Richard Robison of the University of Kansas and The Ohio State University’s Loren Babcock in a paper published in the Nov. 30, 2011, issue of the online journal Paleontological Contributions.

“This trilobite was named after me in acknowledgment of the work my students and I have done on the local Cambrian rocks,” says Liddell, head of USU’s Department of Geology.

Barely an inch long, tiny Z. liddelli lived about 520 million years ago and experienced a landscape much different from today’s Utah.

“During the Cambrian period, Utah was situated within five degrees of the equator,” Liddell says. “The current Wellsville Mountains didn’t yet exist. Instead, this area was covered by a shallow ocean with a warm, tropical climate.”

Z. liddelli was likely a sediment-processor, he says, subsisting mostly on algae. The diminutive invertebrate might have been pursued by larger, carnivorous arthropods such as the shrimp-like Anomalocaris or the bizarre, multi-tentacled Hallucigenia.  

“The trilobite’s spiny exterior was probably its best defense against predators,” Liddell says. “Nobody would want to take a bite out of that.”

Z. liddelli is among a profusion of trilobites, ranging in size from about a millimeter to the length of a skateboard, that flourished during the Cambrian period. The hard-shelled, segmented creatures roamed oceans of the lower Paleozoic era for more than 270 million years.

“Fossils of between 50 to 60 trilobite species have been found in the Spence Shale of the Wellsvilles,” Liddell says. “

The three-lobed arthropods, among the world’s first creatures with compound eyes, eventually died out at the end of the Permian period.

The Wellsville Mountains offer several locations of exposed layers of Cambrian rocks and, thus, an ideal study site for Liddell and his students.

“In the slopes above present-day Honeyville and Brigham City, we’ve identified seven cyclical ‘packages’ or groups of similar rocks,” Liddell says. “These allowed us to develop a mathematical model, by which we can predict the locations of fossil assemblages.”

Earth scientists studying the area now routinely refer to “Liddell Cycle 5” or “Liddell Cycle 7” in research reports. Amateurs also enjoy fossil findings.

“There’s plenty of fossils for everyone and, in fact, we encourage rockhounds to explore the area and let us know of their discoveries,” Liddell says. “And the area affords breathtaking views of the Bear River Bird Refuge and Brigham City from the Wellsvilles’ western slope.”

He urges caution, however, in exploring the steep, slippery areas that rise to 8,000 feet.

“During a recent field trip to Antimony Canyon overlooking Honeyville, my students and I hiked into the mountains only to be caught in a sudden snow squall and icy conditions,” he says. “We made it back without incident, but you always have to be prepared for the unexpected.”

Related links:

USU Department of Geology

USU College of Science

Contact: Dave Liddell, 435-797-1261,

Writer: Mary-Ann Muffoletto, 435-797-3517,

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